Not just because between them those companies are responsible for half New Zealand greenhouse gas emissions, meaning they can, if they put their minds to it, make a real difference.

It’s also the fact that they are prepared to stand up as a group and say this problem is serious, it’s urgent and we need to act.

Cynics are wary of greenwashing, and I can understand why. The time to take action was 30 years ago – it’s not as if knowledge that human activity is warming the planet is new.

And it’s not like corporate New Zealand has had a good record to date; New Zealand’s greenhouse gas emissions have soared over the past 30 years (in 2016, our net emissions in were 54% higher than they were in 1990) at the very time when internationally, we were making promises to cut them.

Nevertheless, we are where we are today, and the problem is now so great that it requires every single one of us – including chief executives – to do whatever we can to keep the impacts of climate change to a minimum.

So to see the heads of 60 companies like Air New Zealand, Fonterra, KiwiRail, Westpac and Z Energy sign the Climate Leaders’ Declaration is welcome.

Now all they have to do is put it into practice.

The declaration says that signatories support the Paris Agreement on climate change, will measure and publicly report their greenhouse gas emissions, and will reduce them in line with keeping global warming to no more than two degrees.

On this I disagree with them. We need to do better than that. Clear evidence is emerging that the impacts on humans and on nature are vastly higher at 2C of warming (think sea-level rise possibly as high as six metres) than they are at 1.5Cof warming.

Both targets are in the Paris Agreement. The 2C target is the one that gets the most attention, but the 1.5C so-called “aspirational” limit, introduced at the instance of small-island nations who are facing the largest and most urgent climate impacts, is the one that really matters.

The world is already 1.1C warmer than it was before the start of the Industrial Revolution. This summer we’ve seen what even that amount of warming can do, with heatwaves and intense storms hitting the country, and species like little blue penguins dying and albatross chicks failing to hatch.

The impacts of climate change increase exponentially as global average temperatures rise. We don’t have enough research in this country to tell us exactly what the effects on native species are likely to be, but international science tells us that it’s likely to be twice as bad with 2C of warming than it is at 1.5C of warming.

The International Panel on Climate Change is due to release a report soon on the 1.5deg target, but leaked reports suggest that we could reach 1.5C of warming by 2040.

Which means we have only a few years – probably as little as eight to 10 – to make deep, sustained emissions cuts.

Which brings us back to the Climate Leaders Coalition and their declaration. Making a public stand on climate change is a good start. Promising to cut greenhouse gas emissions is better (notwithstanding what I have said about the 2C target).

But none of it means anything if they don’t actually do the hard yards and cut their emissions. Seriously, and on a scale that actually protects us and nature from the worst impacts of climate change.

So today I’m going to make my own pledge, an Environmental Leader’s Declaration:

Climate change is the single biggest threat that humans and nature face.

I support the Paris Agreement’s goal of keeping warming to no more than 1.5C.

My team and I will support and work with any chief executive seriously committed to taking action on climate change.

We will call out companies that fail to deliver on their promises.

And to companies that have not yet signed the up to the Climate Leaders’ Coalition, I say: “citizens and consumers deserve to know who is taking serious action on climate change, and who is not: we’re watching you, too.”

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